1. Field of the Invention
The present invention generally relates to a mobile communication system. More particularly, the present invention relates to a method for transmitting and receiving a Forward Shared Control CHannel (F-SCCH) message to support a variety of antenna technologies for data transmission in a Multiple Input Multiple Output (MIMO) mobile communication system.
2. Description of the Related Art
Mobile communication systems are evolving to high-speed, high-quality wireless packet data communication systems that additionally provide data service and multimedia service beyond the early-stage voice service. Many mobile communication standards such as 3rd Generation Partnership Project (3GPP) High Speed Downlink Packet Access (HSDPA), 3GPP High Speed Uplink Packet Access (HSUPA), 3rd Generation Partnership Project 2 (3GPP2) High Rate Packet Data (HRPD), and Institute of Electrical and Electronics Engineers (IEEE) 802.16e have recently been developed to support high-speed, high-quality wireless packet data service.
3rd Generation (3G) wireless packet data communication systems use Adaptive Modulation and Coding (AMC) and channel sensitive scheduling in order to increase transmission efficiency. With AMC, a transmitter can control the amount of transmission data according to channel status. For a receiver in a poor channel status environment, the transmitter transmits less data to the receiver to thereby maintain a reception error probability at an acceptable level. For a receiver in a good channel status environment, the transmitter transmits more data to the receiver so as to achieve a desired reception error probability and enable efficient transmission of a large volume of data. Channel sensitive scheduling is a scheme in which the transmitter selects a user in a good channel status environment from among a plurality of users and provides services to the user. Compared to allocating a channel to one user and providing services to the user, the channel sensitive scheduling increases system capacity. This system capacity increase is called a multi-user diversity gain. That is, the AMC and channel sensitive scheduling schemes apply an appropriate Modulation and Coding Scheme (MCS) at a time that is considered most efficient, based on channel status information fed back from the receiver.
Both the AMC and the channel sensitive scheduling schemes are based on the premise that the receiver feeds back its channel status information, referred to as a Channel Quality Indicator (CQI), to the transmitter.
Shifting from a multiple access scheme used for 2nd Generation (2G) and 3G mobile communication systems, Code Division Multiple Access (CDMA) to Orthogonal Frequency Division Multiple Access (OFDMA) is an active study area in future-generation systems. The 3GPP and the 3GPP2 are working on standardizing evolved OFDMA systems. It is known that OFDMA increases capacity, compared to CDMA. One of many factors that bring the capacity increase is frequency-domain scheduling. As the channel sensitive scheduling offers a capacity gain based on the time-variant characteristics of channels, a higher capacity gain can be achieved by utilizing the property that channels have different characteristics in frequency. In order to support the frequency-domain scheduling, the transmitter should have knowledge of the channel status of each frequency. That is, the transmitter needs a CQI feedback for each frequency, thus increasing CQI feedback overhead.
MIMO is also under active study in the future-generation systems. MIMO is a technology for transmitting/receiving a plurality of data streams through multiple transmit/receive antennas using the same resources. It is said that for a receiver in a good channel status environment, more data is transmitted in a plurality of data streams with a lower modulation order than in a data stream with a high modulation order, under the same error probability. In MIMO, the dimension in which each data stream is transmitted is called a layer. Capacity is efficiently increased by separately applying AMC to individual layers according to their channel statuses. For example, Per Antenna Rate Control (PARC) transmits different data streams through different transmit antennas. Here, each layer corresponds to a transmit antenna. A plurality of transmit antennas experience different channels and PARC applies AMC such that more data can be transmitted through a transmit antenna in a good channel status and less data through a transmit antenna in a poor channel status. Another example of independent AMC application to different transmit antennas is Per Common Basis Rate Control (PCBRC). In PCBRC, each layer corresponds to a fixed transmission beam. PCBRC transmits more data by a transmission beam in a good channel status environment and less data by a transmission beam in a poor channel status environment.
In general, control information is transmitted and received on an F-SCCH in a mobile communication system. The F-SCCH is transmitted along with data to a Mobile Station (MS), carrying control information required for data demodulation. Fields of the F-SCCH will be described with reference to Table 1 below. Table 1 illustrates an exemplary format of an F-SCCH message. In addition to the fields listed in Table 1, other fields can be added or the number of bits of each field may vary.
TABLE 1FieldBlock typeMACIDPersistentChanIDPFExt. TxRankNumber 29-1116-84-612of bitsFLAM00111110MCW01111110FLAM1MCW10100310FLAM2SCW11111111FLAM
In Table 1, Block type indicates the type of the F-SCCH message. Medium Access Control IDentifier (MACID) provides a MAC ID identifying an MS. Upon receipt of the F-SCCH message, the MS compares the received MAC ID with its MAC ID to determine whether data is intended for the MS. While the MAC ID is included in the F-SCCH message in Table 1, the F-SCCH message can be scrambled with a scrambling sequence specific to the MAC ID of the MS that will receive the F-SCCH message. Persistent is a field indicating whether resources allocated to the MS are fixed or variable.
ChanID (Channel IDentifier) identifies the resources allocated to the MS. PF (Packet Format) indicates a code rate and a modulation order such as Quadrature Phase Shift Keying (QPSK), 8PSK (8-ary PSK), or 16QAM (16-ary Quadrature Amplitude Modulation). Ext. Tx (Extended Transmission) indicates the time duration of transmission data. Rank is the number of data streams transmitted through a plurality of antennas.
FLAM (Forward Link Assignment Message) indicates that the F-SCCH message is for allocating downlink resources. MCW (Multi CodeWord) indicates that when a plurality of data streams are transmitted through a plurality of antennas, the data streams include codewords resulting from independent channel coding (e.g. turbo coding). SCW (Single CodeWord) indicates that when a plurality of data streams are transmitted through a plurality of antennas, each of the data streams includes part of a codeword resulting from a single channel coding. In Table 1, FLAM, MCW FLAM1, MCW FLAM2, and SCW FLAM are types of F-SCCH messages.
In Table 1, for each F-SCCH message type, bold numerals are logical values indicating whether the F-SCCH message includes the fields corresponding to the logical values. For example, for FLAM, Rank is 0 (not included), whereas for SCW FLAM, Rank is 1 (included). Because an F-SCCH message being FLAM is transmitted through a single transmit antenna in SIMO (Single Input Multiple Output), the F-SCCH message does not need Rank that is required for transmission of a plurality of data streams. On the contrary, for SCW FLAM, a plurality of data streams can be transmitted and thus Rank is needed.
However, the above conventional F-SCCH message format supports neither precoding that can be used for multiple transmit/receive antennas nor various formats of pilots. When common pilots are used, a precoding scheme used for data should be notified separately. If dedicated pilots are used, the pilot format of the dedicated pilots should be indicated. Accordingly, there exists a need for a technique for notifying a precoding scheme and the format of dedicated pilots by an F-SCCH message.